This invention relates generally to the field of wheelchairs and more particularly to wheelchairs which include adjustable seats to allow the wheelchair occupant to change: position when seated on the wheelchair.
Wheelchairs have been known and used for many years to assist disabled people in moving about. Wheelchairs are comprised of two main components, the mobile platform, which includes the base and wheels, and the seat, which is mounted to the base. In some cases the disabled people may have a problem with one or both legs; in other cases they may have even more serious problems which prevent other limbs from functioning in a coordinated manner. More recently, powered wheelchairs have been developed which include electrically powered drive motors adjacent to the main wheels of the wheelchair. These are particularly helpful to more seriously handicapped people. Typically such drive motors are powered by one or more batteries carried in the lower carriage or platform of the wheelchair.
In the past, the standard design of a wheelchair included large rear wheels and smaller front wheels. This design placed the rims of the rear wheels adjacent to the user""s hands so that hand propulsion was feasible. However, these wheelchair platforms when motorized suffer a disadvantage in that they are not as manoeuvrable as desired. Therefore, more recently power wheelchair platforms have been developed which involve a central or mid-drive wheel, one or more rear pivoting wheels, and front anti-tip idler wheels which generally ride above the ground. An example of this type of wheelchair is produced by Pride Health Care Inc. and is illustrated in U.S. Pat. No. 5,944,131. The stated advantage of this wheelchair platform design is the greater degree of manoeuverability over conventional platforms since the drive wheels are located directly under the occupant at about the middle of the wheelchair. This location of the drive wheels means the turning radius is extremely small because in essence a shorter wheel base is provided. This makes the wheelchair platform more manoeuvrable and easier to get around corners in hallways, through doorways, and the like.
Wheelchair occupants tend to be seated on their wheelchairs for extended periods of time. No matter how carefully the seat and seat cushions are designed, it is still necessary for the occupant to change position from time to time to release pressure on areas at risk of developing pressure sores and to redistribute pressure. Therefore, it has been common to provide seats which are adjustable in position to improve the safety and comfort of the user.
A wheelchair seat is typically comprised of an upright seat back portion and a generally horizontal seat portion, which in the usual position form approximately a 900xc2x0 angle therebetween. The seat frame, comprising the seat back and seat, is usually attached to the wheelchair platform. There are two main types of position of adjustment that can be made to seats, namely, tilt and recline. In a tilt system, the seat back portion and the seat portion remain in a fixed angular relation to one another through a change of angle of the seat frame. Therefore, as the seat back is tilted down at the back, the seat portion is tilted up at the front. In a recline adjustment, the angle between the seat back and the seat changes so that as the seat back portion is reclined, the seat portion remains generally horizontal.
Ideally a seat on a wheelchair platform will be located such that it won""t compromise the stability of the wheelchair, typically with the user""s center of gravity located between the front and rear wheels of the wheelchair. A problem exists with shorter wheelbase wheelchairs when the position of the user is changed relative to the base through seat adjustment. For example, when tilting, the center of gravity of the user will move rearwardly as the seat tilts back. This can lead to an overbalancing of the wheelchair and a dangerous situation for the occupant. Therefore, the prior art discloses examples of center of gravity compensation mechanisms for tilt systems. An example of such a system is U.S. Pat. No. 5,044,647 entitled Stabilized Reclining System. In this system, as the seat tilts, the seat back and seat portion assembly moves forward. This is accomplished by means of a pivot point sliding in a cam. Note that while the title of the invention uses the term xe2x80x9creclinexe2x80x9d all that is taught is a tilt system. This prior invention does not teach any structure to allow the seat back angle to change relative to the seat, with the seat remaining essentially horizontal, as is usually the case for reclining, because the seat and seat back are connected by a substantially rigid connection.
The same problem of the center of gravity changing as the position of the user changes on the wheelchair exists with recline systems, and various attempts have been made in the past to change the position of the user during recline. However, all of these prior systems teach a need to change the elevation of the seat portion and occupant through the recline. This requires complicated link element structures, and makes it more difficult to adjust the position of the seat since in addition to reclining, lifting or the like is required. Further, the structures proposed include multiple link assemblies which are less stable than what is desirable. An example of such a device is found in U.K. Patent Application 2,136,742 to Waite. Other examples of various prior art recline systems include U.S. Pat. No. 5,333,887 to Luther, U.K. Patent Application 2,101,884 to Williams, and U.S. Pat. No. 5,050,899 to Stensby. Other examples of various structures are shown in the following patents:
U.S. Pat. No. 5,853,059 to Goertzen et al.;
U.S. Pat. No. 5,312,153 to Lin;
U.S. Pat. No. 5,154,438 to Barclay;
U.S. Pat. No. 5,108,148 to Henke;
U.S. Pat. No. 5,064,211 to Huttenhuis et al.;
U.S. Pat. No. 5,044,647 to Patterson;
U.S. Pat. No. 4,834,411 to Willey et al.;
U.S. Pat. No. 4,759,561 to Janssen;
U.S. Pat. No. 4,591,182 to Wood;
U.S. Pat. No. 4,346,933 to Jacobs; and
U.S. Pat. No. 3,179,466 to Garrett.
What is desired is a reclining wheelchair which can simply, easily and reliably compensate for changes of position of an occupant""s center of gravity during changes in the position of the seat assembly on the wheelchair platform without changing the elevation of the seat. It is preferred if such a system is a power actuated system and therefore is operable by a disabled person capable only of minor manipulation of motor controls. Ideally such a system would be simple to implement and could be added to any existing power wheelchair platform. Preferably the system would be robust and strong enough to take user and attendant induced stresses and strains without fear of breakage. Lastly, the design should be relatively simple and inexpensive to make.
Therefore, according to the present invention there is provided a kit for adding a reclining seat to a wheelchair, the wheelchair having a base platform with sufficient ground engaging wheels rotatably connected to said base platform to permit said wheelchair to be wheeled along a surface, said kit comprising:
a stationary seat frame for mounting to said base platform;
a seat for mounting to said stationary seat frame, said seat having a seat portion and a back portion pivotally mounted to said seat portion, and an actuator operatively connected to said seat for causing said back portion of said seat to change angle;
a sliding connector for slidably mounting said seat portion to said stationary seat frame; and
means for sliding said seat on said stationary seat frame along said sliding connector without changing height as actuator causes said angle of said back portion to change wherein said kit, when mounted on a wheelchair, compensates for a change in an occupant""s center of gravity as said back portion changes angle by sliding said seat portion on said stationary seat frame.
According to another aspect of the present invention there is provided a wheelchair comprising:
a base platform;
a sufficient number of ground engaging wheels rotatably attached to said base platform to permit said wheelchair to be wheeled along a surface,
a seat mounted on said base platform and having a seat portion and a back portion pivotally attached to said seat portion; and
a recline mechanism operatively connected between the base platform and the seat, the recline mechanism including an adjustable length actuator to cause said seat back portion to change angle, a slidable connection between said seat and said base platform to permit said seat to slide on said base platform without changing height and at least one link element pivotally connected between said seat back portion and said base platform for sliding said seat on said base platform as said angle of said back portion changes, wherein said wheelchair compensates for a change in an occupant""s center of gravity as said seat back portion changes angle.